This invention relates generally to fiber optic communications and, more specifically, to systems and methods for the distribution of signals in a cable television system.
Modern cable television (CATV) distribution systems deliver video programming signals to a large number of subscribers and may additionally provide for the bidirectional transport of digital data (e.g., Internet service), on-demand programming requests (e.g., pay-per-view programming), and voice telephony signals.
A typical CATV system has a headend station that receives satellite signals and converts them to baseband. The headend station may also transmit and receive signals from terrestrially-based communication networks, including the Internet and public switched telephone network (PSTN). Signals received by the headend are combined according to established conventions and optically transmitted to downstream stations using fiber optic cable. Primary and secondary hubs receive the headend optical transmission and amplify it for distribution to nodal stations (nodes) within the CATV distribution plant. Optical signals received by the nodes are converted to radio frequency (RF) electrical signals and transmitted along branches of the system using coaxial cable. Amplifiers, splitters, and taps are typically used to route the RF signals to individual system subscribers.
Bidirectional information flow is achieved by including suitable receivers and transmitters throughout the distribution plant. The receivers and transmitters are designed to transport signals from subscriber equipment, such as modems and set-top boxes, to the headend in the reverse, or upstream, direction. Starting as an RF signal in the 5 MHz -40 MHz band, subscriber-generated information is transmitted to the nodes using coaxial cable. Electrical signals received by the node are converted to optical signals that are transported to the hubs and headend over fiber optic cable.
Known as a hybrid fiber coax (HFC) system, the architecture described above is an industry standard. Combining the low cost and ease of installation of conventional RF cable with the high bandwidth capabilities of optic fiber, these networks can efficiently distribute headend-transmitted digital and analog television signals to a large subscriber base. In conventional systems, signal transport in the reverse direction is complicated by the fact that upstream noise from a large number of sources is combined at the nodes and funneled into hubs and the headend receiver. Electronic interference (ingress) may enter the system at each subscriber location. This interference may be due, at least in part, to leaky connectors. The ingress noise is summed at the nodes and added to distortion in the fiber optic plant, which may be present as a result of diode clipping and intermodulation.
Regardless of signal modulation format, the number of subscribers connected to a single node (referred to as the depth of the fiber in the system) is a major determinant of the noise signal received by a node. Since each item of subscriber equipment can be a source of ingress, the total noise received increases with the number of potential subscribers (e.g., homes passed) that the system serves. Conventional HFC systems have node sizes of 600 to 1200 homes passed and incorporate several RF amplifiers in the coaxial network connecting individual subscribers to a node. Fiber deep architectures offer improved performance by decreasing the number of potential subscribers connected to each node and eliminating the RF amplifiers in the coaxial plant. Optionally, the fiber deep nodes may contain processors for resolving media access control issues.
Fiber deep node reverse plant architectures may utilize multiplexing nodes to combine the signals from several nodes before transmitting the signals to a hub. Alternatively, the nodes may be connected, one to another, with one end of the network connected to a hub in a daisy-chained fashion. The ATandT Lightwire II system, for example, employs two-way digital baseband communication network in which several xe2x80x98mini fiber nodesxe2x80x99, or mFNs, are connected in a daisy chain architecture. Attractive features of this system include ease of expansion and the improved fidelity of digital transmission.
Unfortunately, this prior art architecture has no provision for electronic fault location from the headend station. Therefore, a break in the upstream portion of a string of daisy-chained nodes will disconnect the downstream portion of the chain from the system. Thus, what is needed is an improved system architecture that allows for electronic fault location from the hub or headend station.